1. Field of the Invention
The present invention relates to a fuel injection pump with an electronic governor and a device for advancing a fuel injection timing to a diesel engine when started up in a low temperature, and particularly, to a technology for preventing an operational error of the cold start device.
2. Background Art
Conventionally, there are well-known fuel injection pumps for diesel engines, each comprising a plunger, a plunger barrel, a distribution shaft, and delivery valves, wherein the plunger is vertically reciprocated in the plunger barrel to send pressurized fuel to the distribution shaft, the distribution shaft distributes the fuel from the plunger among the delivery valves, and the delivery valves send fuel to respective fuel injection nozzles. Some of the well-known fuel injection pumps each includes a controller mainly composed of a computer electrically controlling the injection quantity and timing of fuel to the engine. Further, some of the electrically controlled fuel injection pumps each includes a device for advancing a fuel injection timing to a diesel engine when started up in a low temperature (“Cold Start Device”, hereinafter, referred to as “CSD”) for changing the injection timing of fuel, as disclosed in Japanese Laid Open Gazette No. 2000-234576.
The controller controls an electronic governor and the CSD with software previously installed therein and on the basis of signals from a rotary sensor and a water temperature sensor connected to the controller, so as to control the injection quantity and timing of fuel to the engine.
The CSD includes an injection-advancing actuator which is operated by the controller to open and close an overflowing sub port formed in the plunger barrel so as to change the injection timing. More specifically, when an engine in a low temperature is started up, the CSD performs an injection-advancing control to advance the injection timing which is a timing for closing the overflowing sub port, thereby smoothening the start-up of the engine. The controller electrically controls the injection-advancing actuator for opening and closing the overflowing sub port. In this control, the water temperature sensor connected to the controller detects a temperature of cooling water of the engine, and the controller measures the detected temperature of cooling-water. To start up the engine, when the water temperature value measured by the controller is lower than a threshold value of water temperature, i.e., during start-up of the engine in a low temperature, the controller activates the injection-advancing actuator of the CSD so as to perform the injection-advancing control.
However, with respect to a control device including the above-mentioned controller, during start-up of the engine, driving of a selmotor lowers battery voltage, i.e., voltage of a power source of the controller, whereby the controller mismeasures temperature. When the error of measurement becomes large, the controller recognizes a temperature value that is higher than an actual temperature. If the water-temperature value recognized by the controller exceeds the above-mentioned threshold water-temperature value because of the mismeasurement of water-temperature by the controller in which the actual temperature of engine-cooling water is not reflected, the command from the controller to the injection-advancing actuator may be canceled so as to inactivate the CSD, so that the engine cannot be smoothly started up.
This phenomenon will be described with reference to measurement data of FIG. 5.
FIG. 5 graphs variations of an engine rotary speed N, a controller power source voltage (battery voltage) V, and a water-temperature value T recognized by a controller based on a signal from a water-temperature sensor, in relation to time t (water-temperature value T does not always coincide with actual water temperature).
Time t equaling to 0 is defined as a time when a starter is switched on and an engine starts cranking. The cranking is started immediately the controller activated by switching-on of a power source of the controller recognizes a starter signal and starts rotating a selmotor. The moment electric power is applied to the selmotor, voltage of the controller power source is temporarily lowered (as represented by a portion Va in FIG. 5). In this measurement, the minimum of measured lowered controller power source voltage attains 5.3V. During this lowering of the controller power source voltage, the controller mismeasures the water-temperature signal from the water-temperature sensor so as to decide on a high water-temperature value (as represented by a portion Ta in FIG. 5) against actual water-temperature. Consequently, it may happen that the controller cannot recognize a right water-temperature value against the above-mentioned temporary lowering of voltage.
The controller is adapted to cancel the activation command to the CSD when it recognizes the water-temperature rising above a certain preset value (normally, about 5° C.). That is, due to the mismeasurement of the controller about the water-temperature caused by the lowering of battery voltage at the time of cranking of the engine, the controller recognizes the water-temperature rising to about 300C during the short period of lowering the battery voltage, and cancels the activation command to the CSD. In other words, due to the mis-recognition of the controller about the engine-cooling water temperature caused by the lowering of the controller power source voltage, the CSD is misoperated (inactivated) in disregard of the actual cooling-water temperature, thereby inhibiting the engine from being smoothly started up in a low temperature.
An object of the invention is prevention of the misoperation of the CSD during engine-start in a lower temperature caused by the wrong recognition of the controller about cooling-water temperature due to the lowering of the controller power source voltage when an engine is started up, thereby ensuring stable start-up of the engine in a low temperature.